Microfluidic chips with optically transparent glue coating and a method of manufacturing microfluidic chips with optically transparent glue coating for a microfluidic device

ABSTRACT

A microfluidic chip for a microfluidic system includes a PDMS substrate having a first thickness, at least one microfluidic pathway in the substrate, a coating along the microfluidic pathway, and a glass layer having a second thickness on the substrate and above the microfluidic pathway, wherein the coating contains an optically transparent material, and the first thickness is greater than the second thickness. The coating includes cyanoacrylates, an UV curable epoxy adhesive, a gel epoxy or epoxy under trade name of EPO-TEK OG175, MasterBond EP30LV-1 or Locite 0151.

CROSS REFERENCE TO RELATED APPLICATION

The present invention is related to an application, entitled “Continuous Flow Microfluidic Chip With On-Chip Heater And Temperature Sensor, And Microfluidic Device Containing The Same” by Tej Patel, Ryan Revilla and Matthew D'Ooge. The content of this application is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method of manufacturing microfluidic chips for handling fluid samples on a microfluidic level, and, more specifically, to a method of manufacturing microfluidic chips with coating to reduce fluid diffusion and microfluidic chips with a coating to reduce fluid diffusion. The manufactured microfluidic chips can be used to perform real-time analysis, for example, polymerase chain reaction (PCR) analysis.

2. Discussion of the Related Art

Microfluidics can be used in medicine or cell biology researches and refers to the technology that relates to the flow of liquid in channels of micrometer size. At least one dimension of the channel is of the order of a micrometer or tens of micrometers to be considered as microfluidics. In particular, microfluidic devices are useful for manipulating or analyzing micro-sized fluid samples on microfluidic chips, with the fluid samples typically in extremely small volumes down to less than pico liters.

When manipulating or analyzing fluid samples, fluids are pumped onto the micro-channel of microfluidic chips in doses or are continuously flowed onto the micro-channel of microfluidic chips. If the fluid sample is pumped in doses, the fluid sample stays in the micro-channel of the microfluidic chip until the fluid sample is suctioned out from the micro-channel. The fluid sample can be manipulated or analyzed while being held in the micro-channel.

Alternatively, for continuous flow analysis, the fluid is pumped continuously into the micro-channel. Due to the continuous fluid pumping, the fluid sample instead flows and travels through the micro-channel and exits the micro-channel when reaches the outlet of the micro-channel. The fluid sample can be manipulated or analyzed while flowing through the micro-channel, and one can perform a biochemical reaction examination on the continuously flowing fluid sample, including treating and manipulating processes of the fluid.

Presently, microfluidic chips have micro-channels molded in PolyDiMethyiSiloxane (“PDMS”). The micro-channels then are sealed when the PDMS block is bonded to a glass slide.

FIGS. 1A-1D are perspective views of manufacturing a microfluidic chip mold according to the related art. The manufacturing of a microfluidic chip according to the related art takes a channel design and duplicates the channel design onto a photomask 10. As shown in FIG. 1A, a photoresist 22 is deposited onto a semiconductor wafer 20. As shown in FIG. 1B, the photomask 10 that reflects the channel design 12 is placed over the wafer 20, and the wafer 20 with the mask 10 undergoes UV exposition to cure the photoresist 22. Then, as shown in FIG. 1C, the wafer 20 with the cured photoresist 22′ is developed. The ‘negative’ image of a channel according to the channel design is etched away from the semiconductor wafer 20. As shown in FIG. 1D, after all residual photoresist are removed, the resulting wafer becomes a mold 20 that provides the channel according to the channel design 12′.

FIG. 2 are perspective views of the steps of manufacturing a microfluidic chip according to the related art. As shown in FIG. 2, PDMS in liquid form 30 is poured onto the mold 20′. Liquid PDMS 30 may be mixed with crosslinking agent. The mold 20′ with liquid PDMS 30 is then placed into a furnace to harden PDMS 30. As PDMS is hardened, the hardened PDMS block 30′ duplicates the micro-channel 12″ according to the channel design. The PDMS block 30′ then may be separated from the mold 20′. To allow injection of fluid into the micro-channel 12″ (which will subsequently be sealed), inlet or outlet is then made in the PDMS block 30′ by drilling into the PDMS block 30′ using a needle. Then, the face of the PDMS block 30′ with micro-channels and a glass slide 32 are treated with plasma. Due to the plasma treatment, the PDMS block 30 and the glass slide 32 can bond with one another and close the chip.

The microfluidic chip according to the related art has a micro-channel in the PDMS block. PDMS belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicone, and can be deposited onto the master mold in liquid form and subsequently hardened.

However, PDMS is inherently porous and due to its polymer structure, PDMS is highly permeable. Thus, diffusion of fluid sample through PDMS has been observed. Such diffusion of fluid sample does not impact a microfluidic system that pumps fluid samples in doses as significantly as a continuous flow microfluidic system. In particular, when a continuous flow microfluidic system monitors treating and manipulating of the flowing fluid in real-time analysis applications, diffusion or unaccounted loss of fluid sample can significantly impact the real-time analysis. Thus, there exists a need for reducing diffusion or loss of fluid sample in micro-channel of a microfluidic chip.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the invention are directed to a method of manufacturing microfluidic chips for handling fluid samples on a microfluidic level and microfluidic chips that can substantially obviate one or more of the problems due to limitations and disadvantages of the related art.

An object of embodiments of the invention is to provide a method of manufacturing microfluidic chips to reduce fluid diffusion in micro-channel, and microfluidic chips manufactured using the same.

An object of embodiments of the invention is to provide a method of manufacturing microfluidic chips with micro-channel coating, and microfluidic chips manufactured using the same.

Additional features and advantages of embodiments of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of embodiments of the invention. The objectives and other advantages of the embodiments of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purpose of embodiments of the invention, as embodied and broadly described, a microfluidic chip device according to an embodiment of the present invention includes a substrate having a first thickness, at least one microfluidic pathway in the substrate, a coating along the microfluidic pathway, and a glass layer having a second thickness on the substrate and above the microfluidic pathway, wherein the coating contains cyanoacrylates, and the first thickness is greater than the second thickness.

In accordance with another embodiment of the invention, as embodied and broadly described, a microfluidic chip device includes a substrate having a first thickness, at least one microfluidic pathway in the substrate, a coating along the microfluidic pathway, and a glass layer having a second thickness on the substrate and above the microfluidic pathway, wherein the coating contains an optically transparent material, and the first thickness is greater than the second thickness.

In accordance with another embodiment of the invention, as embodied and broadly described, a method for manufacturing a microfluidic chip device includes etching a substrate having a first thickness for forming at least one microfluidic pathway in the substrate, coating the substrate, and bonding a glass layer having a second thickness on the substrate and above the microfluidic pathway, wherein the step of coating includes coating an optically transparent material, and the first thickness is greater than the second thickness.

In accordance with another embodiment of the invention, as embodied and broadly described, a microfluidic chip device includes a coating along the microfluidic pathway, wherein the coating includes cyanoacrylates, an UV curable epoxy adhesive, a gel epoxy or epoxy under trade name of EPO-TEK OG175, MasterBond EP30LV-1 or Locite 0151.

In accordance with another embodiment of the invention, as embodied and broadly described, a method for manufacturing a microfluidic chip device includes etching a substrate having a first thickness for forming at least one microfluidic pathway in the substrate and coating along the microfluidic pathway, wherein the coating includes coating with cyanoacrylates, an UV curable epoxy adhesive, a gel epoxy or epoxy under trade name of EPO-TEK OG175, MasterBond EP30LV-1 or Locite 0151.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of embodiments of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of embodiments of t/he invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of embodiments of the invention.

FIGS. 1A-1D are perspective views of manufacturing a microfluidic chip mold according to the related art.

FIG. 2 illustrates the steps of manufacturing a microfluidic chip according to the related art.

FIG. 3 is a perspective view of a microfluidic chip for a microfluidic system according to an embodiment of the present invention.

FIG. 4 is a side view of the microfluidic chip shown in FIG. 3.

FIG. 5 is a side view of the microfluidic chip according to another embodiment of the present invention.

FIG. 6 is a top view of a heater for a microfluidic chip of a microfluidic system according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.

FIG. 3 is a perspective view of a microfluidic chip for a microfluidic system according to an embodiment of the present invention, and FIG. 4 is a side view of the microfluidic chip shown in FIG. 3. As shown in FIGS. 3 and 4, a microfluidic chip 100 includes a PDMS substrate 110 and a glass layer 120 on the substrate 110. The glass layer 120 may be formed of borosilicate. As shown in FIG. 3, the thickness of the glass layer 120 is much smaller than the thickness of the substrate 110. For instance, the glass layer 120 may have a thickness of about 0.01 inch or less.

The substrate 110 includes micro-channels 130. The micro-channels 130 form a microfluidic pathway, and the channels allow fluid samples to be flowed through therein. The micro-channels 130 may be formed by etching the substrate 110.

After the micro-channels 130 are formed in the substrate 110 but prior to sealing micro-channels 130 with the glass layer 120, the substrate 110 is coated with cyanoacrylates 112 to seal the surface pores of the substrate 110. Cyanoacrylates are acylic resin and are mainly used as adhesives. However, cyanoacrylates are not used as adhesives in the micro-channels of the substrate 110. Instead, cyanoacrylates are allowed to set to form a coating along the micro-channels 130.

When coating the substrate 110, the amount of cyanoacrylates deposited is controlled so as not to fill the micro-channels 130 of the substrate 110. In addition or alternatively, the micro-channels 130 are formed wider and/or deeper in the substrate 110 to account for the subsequent coating thickness of cyanoacrylates 112.

The microfluidic chip 100 further includes heaters 140 a, 140 b and 140 c. For example, the heaters 140 a, 140 b and 140 c may be resistive heating devices, such as thin-film heaters. The heaters 140 a, 140 b and 140 c may be formed by applying a thin film of conductive material directly on the glass layer 120. For example, the heaters 140 a, 140 b and 140 c may include aluminum. More specifically, the heaters 140 a, 140 h and 140 c may have a thickness of about 0.001 inch or less.

The microfluidic chip 100 further includes temperature sensors 150 a, 150 b and 150 c. For example, the temperature sensors 150 a, 150 b and 150 c may be resistance temperature detectors. The temperature sensors 150 a, 150 b and 150 c provide real-time temperature detection to more than one zones or portions of the microfluidic chip 100. The real-time temperature detection is then used to control heaters 140 a, 140 b and 140 c, respectively. As such, the microfluidic chip 100 may have independently-temperature-controlled zones.

A microprocessor (not shown) may be connected to the temperature sensors 150 a, 150 b and 150 c and the heaters 140 a, 140 b and 140 c to provide independently-temperature-controlled zones for the microfluidic chip 100. For example, the microprocessor may implement a control algorithm, such as PID control to receive temperature inputs from the temperature sensors 150 a, 150 b and 150 c and dynamically controls the output of the heaters 140 a, 140 b and 140 c.

For real-time analysis, an optical sensor 160 is further included and can be placed above or below the microfluidic chip 100. The optical sensor 160 provides real-time monitoring of the manipulation of the fluid sample in the micro-channel 130 of the microfluidic chip 100. The same microprocessor (not shown) can also receive and control the optical sensor 160.

FIG. 5 is a side view of the microfluidic chip according to another embodiment of the present invention. In FIG. 5, a microfluidic chip 100′ includes a layer of cured optically transparent material 112′ between a substrate 110′ and a seal layer 120′. As shown in FIG. 3, the thickness of the seal layer 120′ is much smaller than the thickness of the substrate 110′. For instance, the seal layer 120′ may have a thickness of about 0.01 inch or less.

The substrate 110′ includes micro-channels 130′. The micro-channels 130′ form a microfluidic pathway, and the channels allow fluid samples to be flowed through therein. The micro-channels 130′ may be formed by etching the substrate 110′.

After the micro-channels 130′ are formed in the substrate 110′ but prior to sealing micro-channels 130′ with the seal layer 120′, the substrate 110′ is coated with an optically transparent material to seal the surface of the substrate 110′. The optically transparent material is allowed to set or hardened to form the layer of cured optically transparent material 112′. An UV curable epoxy adhesive, a gel epoxy or epoxy under trade name of EPO-TEK OG175, MasterBond EP30LV-1 or Locite 0151 may be used to coat the surface of the substrate 110′.

When coating the substrate 110′, the amount of the optically transparent material deposited are controlled so as not to fill the micro-channels 130′ of the substrate 110′. In addition or alternatively, the micro-channels 130′ are formed wider and/or deeper in the substrate 110′ to account for the subsequent layer of cured optically transparent material 112.

The microfluidic chip 100′ further includes heaters 140 a, 140 b′ and 140 c′. For example, the heaters 140 a′, 140 b′ and 140 c′ may be resistive heating devices, such as thin-film heaters. The heaters 140 a′, 140 b′ and 140 c′ may be formed by applying a thin film of conductive material directly on the seal layer 120′. For example, the heaters 140 a′, 140 b′ and 140 c′ may include aluminum. More specifically, the heaters 140 a′, 140 b′ and 140 c′ may have a thickness of about 0.001 inch or less.

The microfluidic chip 100′ further includes temperature sensors 150 a′, 150 b′ and 150 c′. For example, the temperature sensors 150 a′, 150 b′ and 150 c′ may be resistance temperature detectors. The temperature sensors 150 a′, 150 b′ and 150 c′ provide real-time temperature detection to more than one zones or portions of the microfluidic chip 100′. The real-time temperature detection is then used to control heaters 140 a′, 140 b′ and 140 c′, respectively. As such, the microfluidic chip 100 may have independently-temperature-controlled zones.

A microprocessor (not shown) may be connected to the temperature sensors 150 a′, 150 b′ and 150 c′ and the heaters 140 a′, 140 b′ and 140 c′ to provide independently-temperature-controlled zones for the microfluidic chip 100′. For example, the microprocessor may implement a control algorithm, such as ND control to receive temperature inputs from the temperature sensors 150 a′, 150 b′ and 150 c′ and dynamically controls the output of the heaters 140 a′, 140 b′ and 140 c′.

Although not shown, for real-time analysis, an optical sensor is further included and can be placed above or below the microfluidic chip 100′. The optical sensor provides real-time monitoring of the manipulation of the fluid sample in the micro-channel 130′ of the microfluidic chip 100′. The optical sensor may be controlled by a microprocessor.

FIG. 6 is a top view of a heater for a microfluidic chip of a continuous-flow microfluidic system according to an embodiment of the present invention. As shown in FIG. 6, a thin-film heater 140 for a microfluidic chip of a microfluidic system preferably may include two electrical interface pads 142 a and 142 b. The two electrical interface pads 142 a and 142 b may receive voltage and/or current. More specifically, electrical resistance or heat may be generated by the thin-film heater 140 based on V²/R or I²×R. Such heat may provide temperature to the channels 130 or 130′ shown in FIG. 4 or 5.

Preferably, the thin-film heater 140 is spread above the channels 130 or 130′ evenly to provide consistent heating of the channel below. The thin-film heater 140 may have a line-like shape between the two electrical interface pads 142 a and 142 b. For example, the thin-film heater 140 may have elongated strips that are substantially parallel with one another.

It will be apparent to those skilled in the art that various modifications and variations can be made in the microfluidic chip of embodiments of the invention without departing from the spirit or scope of the invention. Thus, it is intended that embodiments of the invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 

What is claimed:
 1. A device, comprising: a substrate having a first thickness; at least one microfluidic pathway in the substrate, wherein the microfluidic pathway includes channels etched in the substrate; a coating along the microfluidic pathway, and a glass layer having a second thickness on the substrate and above the microfluidic pathway, wherein the coating contains cyanoacrylates, wherein the coating is configured to be coated along the channels while not contacting the glass layer in the microfluidic pathway, said coating thereby not filling the channels; wherein the coating is configured to seal the channels of the microfluidic pathway, while not filling the channels, wherein the coating is not configured to be used as an adhesive in the channels of the substrate, and the first thickness is greater than the second thickness.
 2. The device according to claim 1, wherein the coating is resistant to temperature as high as about 100 degree Celsius.
 3. The device according to claim 1, wherein the coating is formed on a top surface of the substrate after the channels are formed.
 4. The device according to claim 3, further comprising: a heating element on the glass layer and above the microfluidic pathway.
 5. The device according to claim 4, wherein the heating element includes a thin-film heater.
 6. The device according to claim 4, further comprising: a temperature sensor on the heating element.
 7. The device according to claim 6, wherein the temperature sensor includes a resistive temperature device sensor.
 8. The device according to claim 1, wherein the substrate includes PDMS.
 9. A device, comprising: a substrate having a first thickness; at least one microfluidic pathway in the substrate, wherein the microfluidic pathway includes channels etched in the substrate; a coating along the microfluidic pathway, and a glass layer having a second thickness on the substrate and above the microfluidic pathway, wherein the coating contains an optically transparent material, wherein the coating is configured to be coated along the channels while not contacting the glass layer in the microfluidic pathway, said coating thereby not filling the channels; wherein the coating is configured to seal the channels of the microfluidic pathway, while not filling the channels, wherein the coating is not configured to be used as an adhesive in the channels of the substrate, and the first thickness is greater than the second thickness.
 10. The device according to claim 9, wherein the coating is resistant to temperature as high as about 100 degree Celsius.
 11. The device according to claim 9, wherein the coating is formed on a top surface of the substrate after the channels are formed.
 12. The device according to claim 9, wherein the substrate includes PDMS.
 13. A method for manufacturing a device, comprising: etching a substrate having a first thickness for forming at least one microfluidic pathway in the substrate, wherein the microfluidic pathway includes channels etched in the substrate; coating the substrate with the at least one microfluidic pathway; and bonding a glass layer having a second thickness on the substrate and above the microfluidic pathway, wherein the step of coating includes coating an optically transparent material, wherein the coating is coated along the channels while not contacting the glass layer in the microfluidic pathway, said coating thereby not filling the channels; wherein the coating seals the channels of the microfluidic pathway, while not filling the channels, wherein the coating is not used as an adhesive in the channels of the substrate, and the first thickness is greater than the second thickness.
 14. The method according to claim 13, wherein the coating is resistant to temperature as high as about 100 degree Celsius.
 15. The method according to claim 13, wherein the step of etching is performed prior to the step of coating.
 16. The method according to claim 13, further comprising: forming a heating element on the glass layer and above the microfluidic pathway.
 17. The method according to claim 16, wherein the step of forming the heating element includes depositing a conductive material on the glass layer and patterning the conductive material.
 18. The method according to claim 16, further comprising: providing a resistance temperature detector on the heating element.
 19. The method according to claim 13, wherein the substrate includes PDMS. 